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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.spawn"></a><a class="link" href="spawn.html" title="spawn">spawn</a>
</h3></div></div></div>
<p>
        <a class="indexterm" name="boost_asio.indexterm.spawn"></a>
      </p>
<p>
        Start a new stackful coroutine.
      </p>
<p>
        Start a new stackful coroutine that executes on a given executor.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><span class="identifier">Executor</span><span class="special">&gt;&gt;</span>
<span class="keyword">auto</span> <a class="link" href="spawn/overload1.html" title="spawn (1 of 6 overloads)">spawn</a><span class="special">(</span>
    <span class="keyword">const</span> <span class="identifier">Executor</span> <span class="special">&amp;</span> <span class="identifier">ex</span><span class="special">,</span>
    <span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">function</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;(),</span>
    <span class="identifier">constraint_t</span><span class="special">&lt;</span> <span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">||</span><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;</span>  <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
  <span class="emphasis"><em>» <a class="link" href="spawn/overload1.html" title="spawn (1 of 6 overloads)">more...</a></em></span>
</pre>
<p>
        Start a new stackful coroutine that executes on a given execution context.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span>            <span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">::</span><span class="identifier">executor_type</span><span class="special">&gt;&gt;</span>
<span class="keyword">auto</span> <a class="link" href="spawn/overload2.html" title="spawn (2 of 6 overloads)">spawn</a><span class="special">(</span>
    <span class="identifier">ExecutionContext</span> <span class="special">&amp;</span> <span class="identifier">ctx</span><span class="special">,</span>
    <span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">function</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">::</span><span class="identifier">executor_type</span> <span class="special">&gt;(),</span>
    <span class="identifier">constraint_t</span><span class="special">&lt;</span> <span class="identifier">is_convertible</span><span class="special">&lt;</span> <span class="identifier">ExecutionContext</span> <span class="special">&amp;,</span> <span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;</span>  <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
  <span class="emphasis"><em>» <a class="link" href="spawn/overload2.html" title="spawn (2 of 6 overloads)">more...</a></em></span>
</pre>
<p>
        Start a new stackful coroutine, inheriting the executor of another.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><span class="identifier">Executor</span><span class="special">&gt;&gt;</span>
<span class="keyword">auto</span> <a class="link" href="spawn/overload3.html" title="spawn (3 of 6 overloads)">spawn</a><span class="special">(</span>
    <span class="keyword">const</span> <span class="identifier">basic_yield_context</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">ctx</span><span class="special">,</span>
    <span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">function</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;(),</span>
    <span class="identifier">constraint_t</span><span class="special">&lt;</span> <span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">||</span><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;</span>  <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
  <span class="emphasis"><em>» <a class="link" href="spawn/overload3.html" title="spawn (3 of 6 overloads)">more...</a></em></span>
</pre>
<p>
        Start a new stackful coroutine that executes on a given executor.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">StackAllocator</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><span class="identifier">Executor</span><span class="special">&gt;&gt;</span>
<span class="keyword">auto</span> <a class="link" href="spawn/overload4.html" title="spawn (4 of 6 overloads)">spawn</a><span class="special">(</span>
    <span class="keyword">const</span> <span class="identifier">Executor</span> <span class="special">&amp;</span> <span class="identifier">ex</span><span class="special">,</span>
    <span class="identifier">allocator_arg_t</span> <span class="special">,</span>
    <span class="identifier">StackAllocator</span> <span class="special">&amp;&amp;</span> <span class="identifier">stack_allocator</span><span class="special">,</span>
    <span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">function</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;(),</span>
    <span class="identifier">constraint_t</span><span class="special">&lt;</span> <span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">||</span><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;</span>  <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
  <span class="emphasis"><em>» <a class="link" href="spawn/overload4.html" title="spawn (4 of 6 overloads)">more...</a></em></span>
</pre>
<p>
        Start a new stackful coroutine that executes on a given execution context.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">StackAllocator</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span>            <span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">::</span><span class="identifier">executor_type</span><span class="special">&gt;&gt;</span>
<span class="keyword">auto</span> <a class="link" href="spawn/overload5.html" title="spawn (5 of 6 overloads)">spawn</a><span class="special">(</span>
    <span class="identifier">ExecutionContext</span> <span class="special">&amp;</span> <span class="identifier">ctx</span><span class="special">,</span>
    <span class="identifier">allocator_arg_t</span> <span class="special">,</span>
    <span class="identifier">StackAllocator</span> <span class="special">&amp;&amp;</span> <span class="identifier">stack_allocator</span><span class="special">,</span>
    <span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">function</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">ExecutionContext</span><span class="special">::</span><span class="identifier">executor_type</span> <span class="special">&gt;(),</span>
    <span class="identifier">constraint_t</span><span class="special">&lt;</span> <span class="identifier">is_convertible</span><span class="special">&lt;</span> <span class="identifier">ExecutionContext</span> <span class="special">&amp;,</span> <span class="identifier">execution_context</span> <span class="special">&amp;</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;</span>  <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
  <span class="emphasis"><em>» <a class="link" href="spawn/overload5.html" title="spawn (5 of 6 overloads)">more...</a></em></span>
</pre>
<p>
        Start a new stackful coroutine, inheriting the executor of another.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">StackAllocator</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">F</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><span class="identifier">Executor</span><span class="special">&gt;&gt;</span>
<span class="keyword">auto</span> <a class="link" href="spawn/overload6.html" title="spawn (6 of 6 overloads)">spawn</a><span class="special">(</span>
    <span class="keyword">const</span> <span class="identifier">basic_yield_context</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <span class="identifier">ctx</span><span class="special">,</span>
    <span class="identifier">allocator_arg_t</span> <span class="special">,</span>
    <span class="identifier">StackAllocator</span> <span class="special">&amp;&amp;</span> <span class="identifier">stack_allocator</span><span class="special">,</span>
    <span class="identifier">F</span> <span class="special">&amp;&amp;</span> <span class="identifier">function</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span> <span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span> <span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;(),</span>
    <span class="identifier">constraint_t</span><span class="special">&lt;</span> <span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">||</span><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special">&lt;</span> <span class="identifier">Executor</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span class="special">&gt;</span>  <span class="special">=</span> <span class="number">0</span><span class="special">);</span>
  <span class="emphasis"><em>» <a class="link" href="spawn/overload6.html" title="spawn (6 of 6 overloads)">more...</a></em></span>
</pre>
<p>
        The <a class="link" href="spawn.html" title="spawn"><code class="computeroutput"><span class="identifier">spawn</span></code></a>
        function is a high-level wrapper over the Boost.Coroutine library. This function
        enables programs to implement asynchronous logic in a synchronous manner,
        as illustrated by the following example:
      </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">spawn</span><span class="special">(</span><span class="identifier">my_strand</span><span class="special">,</span> <span class="identifier">do_echo</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">detached</span><span class="special">);</span>

<span class="comment">// ...</span>

<span class="keyword">void</span> <span class="identifier">do_echo</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">yield_context</span> <span class="identifier">yield</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">try</span>
  <span class="special">{</span>
    <span class="keyword">char</span> <span class="identifier">data</span><span class="special">[</span><span class="number">128</span><span class="special">];</span>
    <span class="keyword">for</span> <span class="special">(;;)</span>
    <span class="special">{</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">length</span> <span class="special">=</span>
        <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
          <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">yield</span><span class="special">);</span>

      <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">,</span>
          <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">length</span><span class="special">),</span> <span class="identifier">yield</span><span class="special">);</span>
    <span class="special">}</span>
  <span class="special">}</span>
  <span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="comment">// ...</span>
  <span class="special">}</span>
<span class="special">}</span>
</pre>
<h5>
<a name="boost_asio.reference.spawn.h0"></a>
        <span class="phrase"><a name="boost_asio.reference.spawn.requirements"></a></span><a class="link" href="spawn.html#boost_asio.reference.spawn.requirements">Requirements</a>
      </h5>
<p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/impl/spawn.hpp</code>
      </p>
<p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
      </p>
</div>
<div class="copyright-footer">Copyright © 2003-2025 Christopher M.
      Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div>
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